134 PHYSIOLOGY 



days, equivalent to 20-25 months in man, and puberty may 

 occur in the rat at 50 days or later, which corresponds to 50 

 months, a little over four years in man. 



Hatai ('17) has shown that at equivalent ages the general 

 composition of the body in terms of water, sohds, protein, fat 

 and ash is similar in man and several other mammals. 



The results serve to emphasize the well recognized similarity 

 among mammals as a group. 



(a) Technique. Concerning the acuteness of sensation in the 

 rat our information is meagre. The response to some sensory 

 stimuh, especially to sounds, is very marked^ — as is shown by 

 jumping when the hands are clapped, and in some cases by an 

 almost maniacal running and jumping — going on to exhaus- 

 tion—when a bundle of keys is jingled before a cage. Vision 

 in the albino is poor as compared with the strains having pig- 

 mented eyes. It also seems sensitive to vibration. 



The emotional states of the rat are very important and play 

 a leading role. There is therefore a profound difference in general 

 condition between rats that are wild and in fear and those that 

 are tame and gentle. 



If rats are played with every day and handled, they soon 

 come to enjoy the experience, and not only do not offer to bite, 

 but relax when picked up, and lose all tendency to struggle in the 

 hand. Fear and flight reactions completely disappear and the 

 general condition of such rats differs widely, even from those that 

 are moderately tame and can be handled without danger of their 

 biting. Thus Hammett, ('21 i) found that when rats of this half 

 tame group were used for removal of the thyroid apparatus, the 

 mortality was 79 per cent, while the same operation could be 

 made on thoroughly gentle rats, which had been handled for 

 weeks before the event, with a mortality of only 13 per cent. 

 Moreover, when wild Norways were used, the mortality was 

 90 per cent, Hammett ('22). 



It is inferred from this that the best results will be obtained 

 from operations when these are made on thoroughly tame and 

 gentle rats. Further, it is highly probable that all physiological 

 responses are definitely modified by the emotional state of the rat. 



